Within the past various decades, many different types of machinery and apparatus have been devised for magnetically recording information on a suitable track or disc. With the advent of inexpensive computers for home, office and industry use, a demand has developed for magnetic discs which are very precise in construction and operation when employed to store information of virtually any kind of description.
In the manufacture of rigid memory discs, a flat substantially co-planar ring of aluminum is coated with an expoy-based matrix having therein a predetermined amount of magnetically sensitive particles. Typically, such coating is applied to the opposite sides of the aluminum ring so that both sides are capable of carrying information.
The epoxy matrix is cured, and thereafter the opposite surfaces of the disc are polished or ground to provide the required surface finish. To ensure that each such disc surface is capable of retaining information and transferring the same to other discs or devices, it is necessary that the thickness of the coating on each side of the disc be within certain predetermined limits.
Prior polishing or grinding methods have employed the use of polishing pads which were simultaneously brought to bear against the opposite side surfaces of the disc in substantial alignment with each other so that both surfaces are polished at the same time as the disc is rotated. This arrangement many times resulted in one side of the disc being ground or polished too much and the opposite side being ground or polished too little, the aluminum body of the disc thereby being located off center with respect to the coatings on the opposite sides. This has been deemed to be unsatisfactory because, although the total thickness of the disc might be maintained within predetermined limits, the thicknesses of the coatings themselves were unequal and usually not within the prescribed tolerances.